/*
  将下面异步代码使用 Promise 的方法改进
  尽量用看上去像同步代码的方式
  setTimeout(function () {
    var a = 'hello'
    setTimeout(function () {
      var b = 'lagou'
      setTimeout(function () {
        var c = 'I ♥ U'
        console.log(a + b +c)
      }, 10)
    }, 10)
  }, 10)
*/

let t1 = () => { 
  return new Promise((resolve, reject) => {
    setTimeout(function () {
      var a = 'hello'
      resolve(a)
    }, 10)
  })
}

let t2 = () => { 
  return new Promise((resolve, reject) => {
    setTimeout(function () {
      var b = 'lagou'
      resolve(b)
    }, 10)
  })
}

let t3 = () => { 
  return new Promise((resolve, reject) => {
    setTimeout(function () {
      var c = 'I ♥ U'
      resolve(c)
    }, 10)
  })
}

Promise.all([t1(), t2(), t3()]).then(arr => console.log(arr[0] + arr[1] + arr[2]))